Direct pulmonary vascular responses in the conscious newborn lamb.

Electromagnetic flow probes were placed around the right and left pulmonary arteries (RPA and LPA) of nine newborn lambs. Preliminary in vitro and in vivo experiments delineated the accuracy and limitations of this method of flow measurement and the value in vivo of a balloon occlusive zero. Six to nine days after surgery, catheters were placed in the aorta and a branch pulmonary artery permitting simultaneous measurements of RPA and LPA flow, pulmonary arterial pressure, and aortic pressure. Vasoactive agents were injected into one lung, and a shift in blood flow distribution reflected direct active vasoconstruction or vasodilation in that lung. With a normal arterial oxygen tension, acetylcholine had no direct effect on the pulmonary vessels, but indirectly lowered pulmonary resistance via its systemic effects. Histamine was a potent direct pulmonary vasoconstrictor, bradykinin was a weak direct dilator, norepinephrine was a direct constrictor, prostaglandin E1 was a direct dilator, and prostaglandin F2a was a direct constrictor. These results demonstrate the feasibility of isolating the direct pulmonary vascular effects of certain pharmacologic agents using a double pulmonary artery flow probe preparation, agents using a double pulmonary artery flow probe preparation, without the use of anesthetics or extracorporeal perfusion circuits.